Hamburger meat that smells rancid or sour, like vinegar, has probably spoiled; this applies to both cooked and raw hamburger meat. Especially when found in conjunction with other indicators of spoilage, such brown or gray areas on the surface of raw ground beef, an off odor is always a bad sign. If you suspect your hamburger meat is bad, discard it immediately for safety purposes.

Raw hamburger meat, or any variety of ground beef, should be used within two days of purchase. If you freeze your hamburger before this time, it will keep indefinitely at 0 degrees Fahrenheit; however, for optimum quality, aim to use it within four months. Cooked hamburger can be refrigerated for up to four days; it can also be frozen indefinitely, but try to use it within three months for best quality.

To prevent premature spoilage, proper storage is key. Raw meat should be kept refrigerated from the moment you bring it home from the store until you're ready to cook it. Cooked hamburger, on the other hand, can stay at room temperature for up to two hours, or one hour on days above 90 F, before it must be refrigerated. Keep unused hamburger in its original packaging, and leftovers in shallow, airtight containers. If you plan to freeze it long-term, overwrap the original packaging with aluminum foil, or seal leftovers in a heavy-duty freezer bag to minimize freezer burn.

Another opportunity for hamburger to spoil is during improper thawing. Never leave it out on the counter to thaw, as harmful bacteria will grow once the surface of the meat warms to 40 F. The best way to thaw hamburger is in the refrigerator. A faster approach is the cold water method: immerse the package of beef in cold water, changing the water every 15 minutes until thawed. You can also thaw frozen hamburger in the microwave, but this may result in a less-than-optimal texture. For safety purposes, you must immediately cook meat that has been thawed using either the cold water or microwave methods.